Economic response to increasing genetic potential for reproductive performance

Nitter, G.

doi:10.1016/b978-0-408-10134-9.50034-0

Cited by 8 publications

(6 citation statements)

References 14 publications

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“…Theoretical and experimental studies support the conclusion that increased ewe reproductive performance will improve economic efficiency by reducing the overhead costs of lamb production (Nitter, 1987). In Britain, the Meat and Livestock Commission (1987) include ewe reproductive performance in their selection indices for all except terminal sire breeds.…”

Section: Introductionmentioning

confidence: 97%

Direct responses in males and correlated responses for reproduction in females to selection for testicular size adjusted for body weight in young male lambs

Haley¹,

Lee²,

Ritchie³

et al. 1990

Reproduction

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Selection based upon testicular diameter adjusted for body weight at 6, 10 and 14 weeks of age was used to produce two lines of sheep, with either high or low testicular size. Ten generations of selection were carried out and the estimate of the realized heritability of the selection criterion was 0.53 +/- 0.01. There were significant positive correlated responses to selection for testicular diameter at 6, 10 and 14 weeks of age, but the correlated responses in body weight at these ages were negative. In mature females, there were significant negative correlated responses to selection in premating body weight in the 1st, 2nd and 3rd breeding season and in the day of the first oestrus in the 2nd breeding season. Litter size per ewe mated had a small positive correlated response to selection in the second breeding season. This latter response appeared to be due to a positive correlated response in fertility, ewes from the High-line having a significantly higher probability of conceiving to a single mating than those from the Low-line. There was no significant correlated response in ovulation rate or litter size per ewe lambing and the genetic correlation between these traits and the selection criterion is likely to be close to zero. This may be due to the adjustment for body weight used, but it is possible that, in any event, body weight in young rams may be a better predictor of female ovulation rate than testicular diameter. These results do not rule out the possibility that testicular size in rams older than those selected would provide a good predictor of genetic merit for female ovulation rate.

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Section: Introductionmentioning

confidence: 97%

Direct responses in males and correlated responses for reproduction in females to selection for testicular size adjusted for body weight in young male lambs

Haley¹,

Lee²,

Ritchie³

et al. 1990

Reproduction

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show abstract

“…Nitter (46) Nitter used as an example the economic response per unit change of LS in the Merinoland breed in southern Germany under four different production systems and for a wide range of average LS (1.1 to 2.5). In all four production systems, ranging from intensive to extensive, the economic value of extra lambs born was high as long as the average LS did not exceed 1.5.…”

Section: Husbandry Considerationsmentioning

confidence: 99%

Finnsheep and their utilization experiences in temperate conditions

Baker¹

1988

AFSci

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Abstract. The highly prolific Finnsheep (F) has been exported to more than 40 countries around the world to improve the reproductive performance of local breeds through crossbreeding. The infusion of one-half F into local breeds results in a substantial improvement in all reproductive traits with net reproduction (lambs weaned/ewe mated) being increased by about 25 % in the British Isles and Western Europe and by up to 70-100 % in New Zealand, South Africa and the USA. Heterosis for litter size at birth has been low or negligible in a number of crossbreeding studies involving F.Serious reservations have been expressed about the growth, fleece producton and carcass characteristics of F. While F-cross lambs are usually lighter at birth than local breeds, their weaning and post-weaning weights are often very similar, at least partly due to heterosis. Despite the perceived poor live conformation of purebred F, the carcass weight, quality and composition of F-crosses have been very similar to local breeds or crosses. A striking feature of F-cross carcasses is that they have more kidney and less subcutaneous fat than local breeds. This may be a desirable feature of F-cross in extensive, pastoral farming situations to help sheep survive during droughts or periods of low pasture production. The fleece weight of the purebred F is 30-40 % lower than most local breeds, particularly long-wooled breeds. However, the 1/4-F crosses have consistently been only s -l o 5 -10 % lower in fleece weight. Studies have reported comparable, or superior, processing qualities of F-cross wool.F-cross ewes have generally been shown to have superior longevity, overall productivity and economic efficiency than local breeds across a diverserange of environments and farming systems. Some of the problems of integrating a highly prolific genotype into extensive, lowcost, sheep production systems are discussed. F has been utilized in many countries by producing a new synthetic population containing a certain proportion (1/8 to 1/2) ofF ancestry. This approach is usually superior to other crossbreeding options such as stratified crossing or rotational crossing systems.

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“…The trait is very important and assessment of the optimum level of prolificacy for the condi-tions and system of production is a major determinant of productive and economic efficiency in sheep systems (Nitter 1987). The trait is very important and assessment of the optimum level of prolificacy for the condi-tions and system of production is a major determinant of productive and economic efficiency in sheep systems (Nitter 1987).…”

Section: Prolificacymentioning

confidence: 99%

Increasing Small Ruminant Productivity in Semi-arid Areas

Thomson¹,

Thomson²

1988

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Economic response to increasing genetic potential for reproductive performance

Cited by 8 publications

References 14 publications

Direct responses in males and correlated responses for reproduction in females to selection for testicular size adjusted for body weight in young male lambs

Direct responses in males and correlated responses for reproduction in females to selection for testicular size adjusted for body weight in young male lambs

Finnsheep and their utilization experiences in temperate conditions

Increasing Small Ruminant Productivity in Semi-arid Areas

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